Mobile networks such as the GPRS (General Packet Radio System) or UMTS Universal Mobile Telephony System) and the Internet generally do not provide a guaranteed quality of service. The effective instantaneous bandwidth varies with time because of congestions, transmission errors or resource sharing, for instance. In the framework of multimedia streaming over such networks, servers must provide adaptation mechanisms to these variations in order to minimize data losses on the one side and to maximize the quality of the content received by the client on the other side. A classical approach of this problem is known as “Stream Switching”. The same content is encoded by a media encoder into several streams at several bit rates. With respect to the currently available bandwidth, an adequate stream, i.e. having an adequate bit rate with respect to the available bandwidth, is selected to be transmitted to the client via a media server, which operates the corresponding stream switching, for selecting said adequate stream to be sent.